As an inner diameter measuring device for measuring inner diameter of a hollow member, e.g. a device disclosed in the Patent Document 1 is known. In the inner diameter measuring device disclosed in the Patent Document 1, a jig is brought into contact with an inner surface of a pipe to be measured, and by bringing a probe in contact with the jig, the probe is brought indirectly into contact with inner surface of the pipe to be measured. Further, the pipe to be measured is rotated, and displacement of inner surface of the pipe to be measured is measured via the jig.
As a result, the result of the measurement contains error caused by interposition of the jig. Further, because the jig is interposed, a measurement can be performed only on a restricted portion such as an end or near an end of the pipe to be measured. Also, there have been problems in that a complicated structure is involved because the pipe to be measured is rotated, and also, in that the device must be designed in large scale in a case where the pipe to be measured is a long member.
To solve the problems as described above, it is an object of the present invention to provide an inner diameter measuring device, in which there is no need to rotate the pipe to be measured, and it is possible to measure inner diameter of an object to be measured because the device is designed in simple structure.